I am using a PC with onboard sound and optical SPDIF out (optical is nice for eliminating ground loops!) into the Alpine PXA-H701/RUX-C701 setup which has optical inputs and then ananlog outputs for each channel (it can do things like 2xStereo for rear speakers, or even DTS/Dolby is you can output it) then I take the analog outs to my amps (components on JL 300/4) and it seems to work pretty well.
The way I did it is like:
PC/Sound Card --(Optical)--> Alpine DSP --(RCA)--> Amps
I opted to use the DSP at all because i wanted some 'hard' volume control and as far as car-based stuff goes that alpine setup is pretty slick, it really does some cool stuff (but it is pretty damn expensive too!)
I guess you can really do it any way you want, you listed a few ways. See what kind of budget you are on and then you can probably start figuring out the road to take.
As far as your question about the amp with optical input it will for sure support PCM (2-channel audio, prtty standard), and MAYBE support DTS/Dolby (Multi channel), you will need to check specs!
Also remember that an amp with digital inputs just has a DAC inside of it and STILL does the AMP stage in analog just like any other amp.